Circuit arrangement for data stream distribution with conflict resolution

ABSTRACT

The invention relates to a circuit arrangement for data stream distribution with conflict resolution, whereby data streams are transmitted bi-directionally, such that first data stream connection units ( 104   a - 104   n ) and second data stream connection units ( 105   a - 105   m ) serve as both input and output connections. A distribution unit ( 100 ), essentially comprises a matrix switching unit ( 101 ), first intermediate buffer units ( 106   a - 106   n ) and second intermediate buffer units ( 107   a - 107   m ). Information is firstly evaluated in the cell head, which, together with information on the availability of intermediate buffer units, determine when a present data stream cell may be transmitted to a relevant output connection unit.

[0001] The present invention relates to a circuit arrangement and a method for distributing data streams with conflict resolution in accordance with the generic part of claims 1 and 11, as disclosed in U.S. Pat. No. 5,745,489.

[0002] Normally, circuit arrangements for data stream distribution are designed according to the principle of “cross rail distribution”. In this context, data streams applied to one or more input connections are forwarded to one or more output connections.

[0003] Besides this unidirectional method, bidirectional methods are known which permit cross-rail distributor connections to act both as inputs and as outputs. The data streams to be forwarded—particularly bit data streams—exist in known protocols, for example in the known Ethernet V2/IEEE 802.3 protocol. Particularly in the case of bidirectional data stream transmission from one or more inputs/outputs to one or more outputs/inputs, conflicts can arise, since transmitting elements of a data stream precludes elements of a second data stream from being transmitted to the same output or from the same input at exactly the same time.

[0004] Great efforts have therefore been made to eliminate these input/output conflicts, and a number of methods have been proposed for this “conflict resolution” (contention resolution).

[0005] DE 19540160 describes a method for coordinating input-buffered ATM (Asynchronous Transfer Mode) switching centers in order to avoid output blockages. A cross rail distributor matrix operates in an entirely parallel manner, i.e. it switches a plurality of cells from different inputs to different outputs during the same interval of time. Since individual package transmissions by the system are normally entirely independent of one another, it is necessary to prevent a data cell from being connected to the same distributor rail matrix output during the same cell or slot period.

[0006] Conventional conflict resolution (contention resolution) is described in DE 19941851.9-31.

[0007] Apparatuses and methods for conflict resolution perform the following primary tasks, for example:

[0008] (a) Selection of data cells, with it being necessary to determine for each data cell period which data cells need to be connected from which inputs to individual cross-rail distributor matrix outputs. This subsidiary task of conflict resolution resolves any transmission conflicts for a plurality of inputs directed at the same distributor rail matrix output and has one or more of the following features:

[0009] (i) Fairness: all of the inputs directed at the same output need to obtain the same share of the total throughput;

[0010] (ii) High throughput: the operation of conflict resolution and of its fairness algorithms should impair a total system throughput as little as possible;

[0011] (iii) Rapid manner of operation: since a new decision needs to be calculated for each data cell period, the calculation time required needs to be shorter than a cell slot time; and

[0012] (iv) Simple implementability: the conflict resolution unit needs to be able to be implemented as a synchronous finite state machine, with no asynchronous parts being allowed by the data-stream layout regulations; and

[0013] (b) Buffer devices need to be provided in order to buffer data cells which are not forwarded during the current data cell period in order to be able to forward them as appropriate at a later time.

[0014] The two tasks “selection” and “buffering” are thus of very great significance for data stream distribution and need to be performed by appropriate devices in the circuit arrangement.

[0015] DE 19935126.0 describes a cross rail distributor based system which contains an integrated conflict resolution unit. The task of selection is performed in a distributor device itself, while the task of buffering is performed on the basis of the prior art in the access units.

[0016]FIG. 5 shows a circuit arrangement for data stream distribution based on the prior art, where references starting with the digit “5” denote elements such as occur in circuit arrangements for data stream distribution and methods based on the prior art. One or more data stream lines are connected to first data stream connection units 504 a-504 n. Similarly, one or more data stream lines are connected to second data stream connection units 505 a-505 m. Both data stream connection units transmit data to and/or data from corresponding first access units 502 a-502 n and second access units 503 a-503 m. The first access units 502 a-502 n and the second access units 503 a-503 m are thus used both as inputs and as outputs for a central distributor device 500. The first access units 502 a-502 n and the second access units 503 a-503 m are connected to a matrix switching unit 501 contained in the distributor device 500.

[0017] For conflict resolution, it is necessary for the data streams supplied by first and second data stream connection units 504 a-504 n and 505 a-505 m not to be forwarded simultaneously to a single one of the corresponding output access units 502 a-502 n and 503 a-503 m in the same cell timeslot. For this reason, data are buffered in the first access units 502 a-502 n and in the second access units 503 a-503 m. The data stream distribution method in accordance with the prior art is based on data which cannot be forwarded to a desired access unit being buffered in the access unit at which the corresponding data stream arrives.

[0018] The information regarding whether or not a corresponding desired access unit is occupied is ascertained in the distributor device 500, so that relatively long information paths need to be provided between the respective first and second access units 502 a-502 n and 503 a-503 m and the matrix switching unit 501, since data are buffered in the access units 502 a-502 n and 503 a-503 m. Long information paths mean a long time delay which entails a problem in terms of short switching times. Such an arrangement based on the prior art is also described in DE 19935126.0, for example.

[0019] A primary drawback of such circuit arrangements for data stream distribution based on the prior art is that long information paths exist which in turn lengthen the switching times for the data streams.

[0020] Another drawback of apparatuses and methods for data stream distribution based on the prior art is that conventional conflict resolution limits the total data stream volume which can be transmitted.

[0021] It is thus an object of the present invention to provide conflict resolution on the basis of selection of the data input streams and buffering of unforwarded data input streams, where data stream distribution is not slowed down by long information paths between access units and a central matrix switching unit.

[0022] The object is achieved by a circuit arrangement for data stream distribution with conflict resolution in accordance with claim 1 and by a method for distributing data streams in accordance with claim 11.

[0023] The inventive circuit arrangement in accordance with claim 1 and the inventive method in accordance with claim 11 have the primary advantage that data streams can be distributed efficiently without any data cell loss and with a minimal delay.

[0024] Another advantage of the present invention is that a flexible arrangement of appropriate distributor devices is made possible which allows access units to be arranged remotely from a distributor device without obtaining delay times for data stream distribution as a result of long information paths.

[0025] The essence of the invention is a circuit arrangement for data stream distribution in which temporary-buffer units are arranged within a distributor device and in which long information paths are avoided, with provision of return-stream information allowing the temporary-buffer units to be kept small.

[0026] Advantageously, information about an access unit in a distributor device, which information is likewise stored in a cell header, is made available quickly for further processing.

[0027] Another advantage is that data streams are forwarded effectively without data cell losses, with avoidance of data cell losses particularly as a result of access units' buffer capacities being exceeded.

[0028] It is also advantageous to provide a flexible arrangement for distributing data streams.

[0029] The subclaims contain advantageous developments and improvements of the respective subject matter of the invention.

[0030] In line with one preferred development, a matrix switching unit in a distributor device has 24 inputs and 24 outputs.

[0031] In line with another preferred development of the present invention, data cells are buffered such that two data cells are never transmitted to the same access unit simultaneously within the same cell timeslot.

[0032] In line with yet another preferred development of the present invention, data alignment with buffer blocks contained in first and/or second access units is performed.

[0033] In line with yet another preferred development of the present invention, first and second data stream connection units have one or more connections for data lines.

[0034] In line with yet another preferred development of the present invention, information in a data-stream cell, running on in the data-stream direction, regarding the information contained in a distributor-device determination field and the information contained in an access-unit determination field is routed to a particular distributor device and to a particular access unit.

[0035] In line with yet another preferred development, if a predetermined threshold value is exceeded upon reaching a temporary-buffer filling level for temporary-buffer units, opposing-data-stream cells are formed which run in the opposing-data-stream direction and contain a backpressure determination field and a backpressure bit-vector field.

[0036] In line with yet another preferred development of the present invention, the temporary-buffer units are of small design, which allows high data throughputs. Such data throughputs can be in the order of magnitude of several 100 GB/s.

[0037] Exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the description below. In the drawings:

[0038]FIG. 1 shows a circuit arrangement for data stream distribution with conflict resolution in line with the present invention;

[0039]FIG. 2 shows the structure of a data stream which is supplied to access units in the circuit arrangement for data stream distribution in line with FIG. 1;

[0040]FIG. 3 shows the structure of a data stream cell running in the data stream direction;

[0041]FIG. 4 shows the structure of an opposing-data-stream cell running in the opposing-data-stream direction; and

[0042]FIG. 5 shows a circuit arrangement for data stream distribution based on the prior art.

[0043] In the figures, identical references denote components which are the same or have the same function.

[0044]FIG. 1 shows a circuit arrangement for data stream distribution with conflict resolution in line with the present invention.

[0045] In the circuit arrangement for data stream distribution shown in FIG. 1, data streams are supplied to first data stream connection units 104 a-104 n and to second data stream connection units 105 a-105 m. The inventive circuit arrangement and the inventive method permit data streams to be transmitted bidirectionally, so that the first data stream connection units 104 a-104 n and the second data stream connection units 105 a-105 m are used both as input connections and as output connections.

[0046] By way of example, FIG. 1 shows four first data stream connection units 104 a-104 n and four second data stream connection units 105 a-105 m. However, it should be pointed out that two or more first data stream connection units can be connected to two or more second data stream connection units, with i being the sequential index and n being the total number of first data stream connection units, while j is the sequential index and m is the total number of second data stream connection units.

[0047] Besides electrical supply of the data streams which are to be distributed, optical supply lines for the data streams to be distributed are generally also provided to the first and second data stream connection units 104 a-104 n and 105 a-105 m.

[0048] A distributor device 100 essentially comprises a matrix switching unit 101 and first temporary-buffer units 106 a-106 n and second temporary-buffer units 107 a-107 m, the number of first temporary-buffer units 106 a-106 n corresponding to the number of first data stream connection units 104 a-104 n, while the number of second temporary-buffer units 107 a-107 m corresponds to the number of second data stream connection units 105 a-105 m. Data streams which are supplied via the first data stream connection units 104 a-104 n are supplied to the first temporary-buffer units 106 a-106 n via first access units 102 a-102 n, while data streams which are supplied to second data stream connection units 105-105 m are supplied to the second temporary-buffer units 107 a-107 m via second access units 103 a-103 m.

[0049] The data streams are split into data cells, as described below with reference to FIGS. 2 to 4. In this context, the information in the cell header is first evaluated which, together with information about any use of temporary-buffer units, determines whether a current data stream cell can be forwarded directly to an associated output access unit or whether an opposing-data-stream cell is formed which is referred back to the corresponding access unit so as to be evaluated there.

[0050]FIG. 2 shows the structure of a data stream which is supplied to access units in a circuit arrangement for data stream distribution in line with FIG. 1.

[0051] The data stream 200 shown in FIG. 2 comprises data stream cells 201 a-201 g, where k corresponds to the sequential index and g corresponds to the total number of data stream cells. Data stream cells shown are generally based on data packets of fixed length. The data stream cells 201 a-201 g carry the information which is to be transmitted and which is to be distributed in the inventive circuit arrangement, with a data stream cell header being used specifically for determining access units and distributor devices, for example, as will be described below with reference to FIGS. 3 and 4.

[0052]FIG. 3 shows the structure of a data stream cell running in the data stream direction.

[0053] The data stream cell 300 shown in FIG. 3 propagates in the data stream direction 301 and comprises individual fields which are made up of fields in a cell header and data stream information fields 304 a-304 n (i=sequential index). A cell header comprises a distributor-device determination field 302 and an access-unit determination field 303. The distributor-device determination field 302 determines which distributor device 100 needs to be supplied with the data stream cell 300, while the access-unit determination field 303 stipulates which access unit 102 a-102 n or 103 a-103 m needs to be supplied with a data stream cell 300 within a distributor device 100.

[0054]FIG. 4 shows the structure of an opposing-data-stream cell running in the opposing-data-stream direction.

[0055] The opposing-data-stream cell 400 shown in FIG. 4 indicates whether a threshold value is exceeded, which indicates that the temporary-buffer filling level of a corresponding temporary-buffer unit is such that no further data stream cells can be temporarily buffered.

[0056] The opposing-data-stream cell 400 thus propagates in an opposing-data-stream direction 401, with the cell header now, unlike the data stream cell illustrated in FIG. 3, comprising a backpressure determination field 402 and a backpressure bit-vector field 403. The backpressure determination field 402 indicates that a backpressure exists on account of overfilling in a corresponding temporary-buffer unit, while the backpressure bit-vector field 403 indicates that the distributor device 100 is no longer able to transmit cells to the corresponding access units from the access unit to which the original data stream was applied.

[0057] The inventive circuit arrangement for data stream distribution with conflict resolution and the inventive method allow free available memory space in the chip space of the distributor device 100 to be used efficiently by virtue of existing buffer devices being distributed to small temporary-buffer devices corresponding to output access units on the distributor device 100. This significantly reduces any period of time required for maintaining communication with connected chip units.

[0058] The introduction of opposing-data-stream cells 400 ensures that no information in a data stream 200 is lost and that transmission delays are limited. In addition, the distributor device collects and disseminates information about the states of chip units connected to it and uses the information in the backpressure bit-vector field 403 of the opposing-data-stream cell 400 to forward this information.

[0059] Although the present invention has been described above with reference to preferred exemplary embodiments, it is not limited thereto but rather can be modified in a wide variety of ways.

[0060] List of references 100 Distributor device 101 Matrix switching unit 102a, . . . , 102i, First access units (i = sequential . . . 102n index, n = total number) 103a, . . . , 103j, Second access units (j = sequential . . . 103m index, m = total number) 104a, . . . , 104i, First data stream connection units . . . 104n (i = sequential index, n = total number) 105a, . . . , 105j, Second data stream connection units . . . 105m (j = sequential index, m = total number) 106a, . . . , 106i, First temporary-buffer units (i = sequential . . . 106n index, n = total number) 107a, . . . , 107j, Second temporary-buffer units (j = sequential . . . 107m index, m = total number) 200 Data stream 201a, . . . , 201k, Data stream cells (k = sequential . . . 201g index, g = total number) 300 Data stream cell 301 Data stream direction 302 Distributor device determination field 303 Access-unit determination field 304a, . . . , 304i, Data stream information fields (i = sequential . . . 304n index, n = total number) 400 Opposing-data-stream cell 401 Opposing-data-stream direction 402 Backpressure determination field 403 Backpressure bit-vector field 500 Distributor device (references starting with the digit “5” denote elements based on the prior art for describing FIG. 5) 501 Matrix switching unit 502a, . . . , 502i, First access units (i = sequential . . . 502n index, n = total number) 503a, . . . , 503j, Second access units (j = sequential . . . 503m index, m = total number) 504a, . . . , 504i, First data stream connection units . . . 504n (i = sequential index, n = total number) 505a, . . . , 505j, Second data stream connection units . . . 505m (j = sequential index, m = total number) 506a, . . . , 506i, First temporary-buffer units (i = sequential . . . 506n index, n = total number) 507a, . . . , 507j, Second temporary-buffer units (j = sequential . . . 507m index, m = total number) 

1. A circuit arrangement for data stream distribution with conflict resolution, having a) a distributor device (100) which has (i) a matrix switching unit (101); (ii) first temporary-buffer units (106 a-106 n); and (iii) second temporary-buffer units (107 a-107 m); b) first data-stream connection units (104 a-104 n) for inputting and/or outputting first data streams; c) second data-stream connection units (105 a-105 m) for inputting and/or outputting second data streams; d) first access units (102 a-102 n) for connecting the first data-stream connection units (104 a-104 n) to the first temporary-buffer units (106 a-106 n); and e) second access units (103 a-103 m) for connecting the second data-stream connection units (105 a-105 m) to the second temporary-buffer units (107 a-107 m); characterized in that opposing-data-stream cells (400) are provided which run in an opposing-data-stream direction (401) and contain a backpressure determination field (402) and a backpressure bit-vector field (403).
 2. The circuit arrangement as claimed in claim 1, characterized in that a matrix switching unit in a distributor device has 24 inputs and 24 outputs.
 3. The circuit arrangement as claimed in one or both of claims 1 and 2, characterized in that the first [lacuna] (104 a-104 n) each have one or more connections for data lines.
 4. The circuit arrangement as claimed in one or more of claims 1 to 3, characterized in that the second data-stream connection units (105 a-105 m) each have one or more connections for data lines.
 5. The circuit arrangement as claimed in one or more of claims 1 to 4, characterized in that optical supply lines for the data streams which are to be distributed are provided for the first and second data-stream connection units (104 a-104 n) and (105 a-105 m).
 6. The circuit arrangement as claimed in one or more of claims 1 to 5, characterized in that data-stream cells are in the form of data packets of fixed length.
 7. The circuit arrangement as claimed in one or more of claims 1 to 6, characterized in that the distributor device is provided as a router in a switching center.
 8. The circuit arrangement as claimed in one or more of claims 1 to 7, characterized in that the first and second temporary-buffer units (106 a-106 n, 107 a-107 m) are provided in isolation according to target outputs.
 9. The circuit arrangement as claimed in one or more of claims 1 to 8, characterized in that the first and second temporary-buffer units (106 a-106 n, 107 a-107 m) are provided according to priorities for a data-stream distribution.
 10. The circuit arrangement as claimed in one or more of claims 1 to 9, characterized in that the first and second temporary-buffer units (106 a-106 n, 107 a-107 m) are provided according to data-stream cell sizes.
 11. A method for distributing data streams with conflict resolution, having the following steps: a) first data streams are input into and/or output from first data-stream connection units (104 a-104 n); b) second data streams are input into and/or output from second data-stream connection units (105 a-105 m); c) the first data streams are temporarily buffered in first temporary-buffer units (106 a-106 n); d) the second data streams are temporarily buffered in second temporary-buffer units (107 a-107 m); and e) the first and second data streams are distributed in a distributor device (100) such that no data-stream conflicts arise; characterized in that opposing-data-stream cells (400) are formed, if a predetermined threshold value is exceeded upon reaching a temporary-buffer filling level for a specific temporary-buffer unit (106 a-106 n, 107 a-107 m), which run in the opposing-data-stream direction (401) and contain a backpressure determination field (402) and a backpressure bit-vector field (403).
 12. The method as claimed in claim 11, characterized in that data cells are temporarily buffered such that two data cells are never transmitted to the same access unit simultaneously within the same cell timeslot.
 13. The method as claimed in one or both of claims 11 and 12, characterized in that data alignment with buffer blocks contained in first and/or second access units is performed.
 14. The method as claimed in one or more of claims 11 to 13, characterized in that information in a data-stream cell, running on in the data-stream direction, regarding the information contained in a distributor-device determination field (302) and the information contained in an access-unit determination field (303) is routed to a particular distributor device and to a particular access unit. 